misc.c

elinux jffs初始版本 具体了解JFFS的文件系统！

		nl_day = day;
		month = 2;
	}
	else {
		nl_day = (year & 3) || day <= 59 ? day : day-1;
		for (month = 0; month < 12; month++)
			if (day_n[month] > nl_day) break;
	}
	*date = nl_day-day_n[month-1]+1+(month << 5)+(year << 9);
}


/* Returns the inode number of the directory entry at offset pos. If bh is
   non-NULL, it is brelse'd before. Pos is incremented. The buffer header is
   returned in bh. */

int fat_get_entry(struct inode *dir, loff_t *pos,struct buffer_head **bh,
    struct msdos_dir_entry **de)
{
	struct super_block *sb = dir->i_sb;
	int sector, offset;

	while (1) {
		offset = *pos;
		PRINTK (("get_entry offset %d\n",offset));
		if ((sector = fat_smap(dir,offset >> SECTOR_BITS)) == -1)
			return -1;
		PRINTK (("get_entry sector %d %p\n",sector,*bh));
		if (!sector)
			return -1; /* beyond EOF */
		*pos += sizeof(struct msdos_dir_entry);
		if (*bh)
			fat_brelse(sb, *bh);
		PRINTK (("get_entry sector apres brelse\n"));
		if (!(*bh = fat_bread(sb, sector))) {
			printk("Directory sread (sector 0x%x) failed\n",sector);
			continue;
		}
		PRINTK (("get_entry apres sread\n"));
		*de = (struct msdos_dir_entry *) ((*bh)->b_data+(offset &
		    (SECTOR_SIZE-1)));
		return (sector << MSDOS_DPS_BITS)+((offset & (SECTOR_SIZE-1)) >>
		    MSDOS_DIR_BITS);
	}
}


/*
 * Now an ugly part: this set of directory scan routines works on clusters
 * rather than on inodes and sectors. They are necessary to locate the '..'
 * directory "inode". raw_scan_sector operates in four modes:
 *
 * name     number   ino      action
 * -------- -------- -------- -------------------------------------------------
 * non-NULL -        X        Find an entry with that name
 * NULL     non-NULL non-NULL Find an entry whose data starts at *number
 * NULL     non-NULL NULL     Count subdirectories in *number. (*)
 * NULL     NULL     non-NULL Find an empty entry
 *
 * (*) The return code should be ignored. It DOES NOT indicate success or
 *     failure. *number has to be initialized to zero.
 *
 * - = not used, X = a value is returned unless NULL
 *
 * If res_bh is non-NULL, the buffer is not deallocated but returned to the
 * caller on success. res_de is set accordingly.
 *
 * If cont is non-zero, raw_found continues with the entry after the one
 * res_bh/res_de point to.
 */


#define RSS_NAME /* search for name */ \
    done = !strncmp(data[entry].name,name,MSDOS_NAME) && \
     !(data[entry].attr & ATTR_VOLUME);

#define RSS_START /* search for start cluster */ \
    done = !IS_FREE(data[entry].name) \
      && ( \
           ( \
             (MSDOS_SB(sb)->fat_bits != 32) ? 0 : (CF_LE_W(data[entry].starthi) << 16) \
           ) \
           | CF_LE_W(data[entry].start) \
         ) == *number;

#define RSS_FREE /* search for free entry */ \
    { \
	done = IS_FREE(data[entry].name); \
	if (done) { \
	    inode = iget(sb,sector*MSDOS_DPS+entry); \
	    if (inode) { \
	    /* Directory slots of busy deleted files aren't available yet. */ \
		done = !MSDOS_I(inode)->i_busy; \
		iput(inode); \
	    } \
	} \
    }

#define RSS_COUNT /* count subdirectories */ \
    { \
	done = 0; \
	if (!IS_FREE(data[entry].name) && (data[entry].attr & ATTR_DIR)) \
	    (*number)++; \
    }

static int raw_scan_sector(struct super_block *sb,int sector,const char *name,
    int *number,int *ino,struct buffer_head **res_bh,
    struct msdos_dir_entry **res_de,char scantype)
{
	struct buffer_head *bh;
	struct msdos_dir_entry *data;
	struct inode *inode;
	int entry,start,done;

	if (!(bh = fat_bread(sb,sector)))
		return -EIO;
	data = (struct msdos_dir_entry *) bh->b_data;
	for (entry = 0; entry < MSDOS_DPS; entry++) {
/* RSS_COUNT:  if (data[entry].name == name) done=true else done=false. */
		if (name) {
			RSS_NAME
			if (done && scantype) {   /* scantype != SCAN_ANY */
				done = (data[entry].attr & ATTR_HIDDEN)
					? (scantype==SCAN_HID)
					: (scantype==SCAN_NOTHID);
			}
		} else {
			if (!ino) RSS_COUNT
			else {
				if (number) RSS_START
				else RSS_FREE
			}
		}
		if (done) {
			if (ino) *ino = sector*MSDOS_DPS+entry;
			start = CF_LE_W(data[entry].start);
			if (MSDOS_SB(sb)->fat_bits == 32) {
				start |= (CF_LE_W(data[entry].starthi) << 16);
			}
			if (!res_bh)
				fat_brelse(sb, bh);
			else {
				*res_bh = bh;
				*res_de = &data[entry];
			}
			return start;
		}
	}
	fat_brelse(sb, bh);
	return -ENOENT;
}


/*
 * raw_scan_root performs raw_scan_sector on the root directory until the
 * requested entry is found or the end of the directory is reached.
 */

static int raw_scan_root(struct super_block *sb,const char *name,int *number,int *ino,
    struct buffer_head **res_bh,struct msdos_dir_entry **res_de,char scantype)
{
	int count,cluster;

	for (count = 0; count < MSDOS_SB(sb)->dir_entries/MSDOS_DPS; count++) {
		if ((cluster = raw_scan_sector(sb,MSDOS_SB(sb)->dir_start+count,
		    name,number,ino,res_bh,res_de,scantype)) >= 0) return cluster;
	}
	return -ENOENT;
}


/*
 * raw_scan_nonroot performs raw_scan_sector on a non-root directory until the
 * requested entry is found or the end of the directory is reached.
 */

static int raw_scan_nonroot(struct super_block *sb,int start,const char *name,
    int *number,int *ino,struct buffer_head **res_bh,struct msdos_dir_entry
    **res_de,char scantype)
{
	int count,cluster;

#ifdef DEBUG
	printk("raw_scan_nonroot: start=%d\n",start);
#endif
	do {
		for (count = 0; count < MSDOS_SB(sb)->cluster_size; count++) {
			if ((cluster = raw_scan_sector(sb,(start-2)*
			    MSDOS_SB(sb)->cluster_size+MSDOS_SB(sb)->data_start+
			    count,name,number,ino,res_bh,res_de,scantype)) >= 0)
				return cluster;
		}
		if (!(start = fat_access(sb,start,-1))) {
			fat_fs_panic(sb,"FAT error");
			break;
		}
#ifdef DEBUG
	printk("next start: %d\n",start);
#endif
	}
	while (start != -1);
	return -ENOENT;
}


/*
 * raw_scan performs raw_scan_sector on any sector.
 *
 * NOTE: raw_scan must not be used on a directory that is is the process of
 *       being created.
 */

static int raw_scan(struct super_block *sb, int start, const char *name,
    int *number, int *ino, struct buffer_head **res_bh,
    struct msdos_dir_entry **res_de, char scantype)
{
	if (start) return raw_scan_nonroot
		(sb,start,name,number,ino,res_bh,res_de,scantype);
	else return raw_scan_root
		(sb,name,number,ino,res_bh,res_de,scantype);
}


/*
 * fat_parent_ino returns the inode number of the parent directory of dir.
 * File creation has to be deferred while fat_parent_ino is running to
 * prevent renames.
 */

int fat_parent_ino(struct inode *dir,int locked)
{
	static int zero = 0;
	int error,curr,prev,nr;

	PRINTK(("fat_parent_ino: Debug 0\n"));
	if (!S_ISDIR(dir->i_mode)) panic("Non-directory fed to m_p_i");
	if (dir->i_ino == MSDOS_ROOT_INO) return dir->i_ino;
	if (!locked) fat_lock_creation(); /* prevent renames */
	if ((curr = raw_scan(dir->i_sb,MSDOS_I(dir)->i_start,MSDOS_DOTDOT,
	    &zero,NULL,NULL,NULL,SCAN_ANY)) < 0) {
		if (!locked) fat_unlock_creation();
		return curr;
	}
	PRINTK(("fat_parent_ino: Debug 1 curr=%d\n", curr));
	if (!curr) nr = MSDOS_ROOT_INO;
	else {
		PRINTK(("fat_parent_ino: Debug 2\n"));
		if ((prev = raw_scan(dir->i_sb,curr,MSDOS_DOTDOT,&zero,NULL,
		    NULL,NULL,SCAN_ANY)) < 0) {
			PRINTK(("fat_parent_ino: Debug 3 prev=%d\n", prev));
			if (!locked) fat_unlock_creation();
			return prev;
		}
		PRINTK(("fat_parent_ino: Debug 4 prev=%d\n", prev));
		if (prev == 0 && MSDOS_SB(dir->i_sb)->fat_bits == 32) {
			prev = MSDOS_SB(dir->i_sb)->root_cluster;
		}
		if ((error = raw_scan(dir->i_sb,prev,NULL,&curr,&nr,NULL,
		    NULL,SCAN_ANY)) < 0) {
			PRINTK(("fat_parent_ino: Debug 5 error=%d\n", error));
			if (!locked) fat_unlock_creation();
			return error;
		}
		PRINTK(("fat_parent_ino: Debug 6 nr=%d\n", nr));
	}
	if (!locked) fat_unlock_creation();
	return nr;
}


/*
 * fat_subdirs counts the number of sub-directories of dir. It can be run
 * on directories being created.
 */

int fat_subdirs(struct inode *dir)
{
	int count;

	count = 0;
	if ((dir->i_ino == MSDOS_ROOT_INO) &&
	    (MSDOS_SB(dir->i_sb)->fat_bits != 32)) {
		(void) raw_scan_root(dir->i_sb,NULL,&count,NULL,NULL,NULL,SCAN_ANY);
	} else {
		if ((dir->i_ino != MSDOS_ROOT_INO) &&
		    !MSDOS_I(dir)->i_start) return 0; /* in mkdir */
		else (void) raw_scan_nonroot(dir->i_sb,MSDOS_I(dir)->i_start,
		    NULL,&count,NULL,NULL,NULL,SCAN_ANY);
	}
	return count;
}


/*
 * Scans a directory for a given file (name points to its formatted name) or
 * for an empty directory slot (name is NULL). Returns an error code or zero.
 */

int fat_scan(struct inode *dir,const char *name,struct buffer_head **res_bh,
    struct msdos_dir_entry **res_de,int *ino, char scantype)
{
	int res;

	res = raw_scan(dir->i_sb,MSDOS_I(dir)->i_start,
		       name, NULL, ino, res_bh, res_de, scantype);
	return res<0 ? res : 0;
}